The following paragraphs lifted from
The Star League (1630) shed some light on this topic:
Well-equipped bases are essential to any miitary. Bases provide a place to store supplies, a place to rest and to call ome, and a defensive position where a unit can hold off attackers until help arrives.
The Star League had thousands of military bases throughout the Inner Sphere and the Periphery. Each inhabited planet had at least one SLDF base or depot. The Border Guards Agreement, signed by the Council Lords in 2572, gave the Star League Defense Forces the right to purchase land on any world. Though the presence of foreign soldiers irked some of the Council Lords, the Reunification War and the rebels' near success convinced everyone to give the SLDF unrestricted range.
The Generals' highest priority in locating bases was to establish circles of defense around Terra. Three defensive rings were built. The innermost, sometimes called the Home Circle, was the heavily fortified border of the Terran Hegemony. Bases in the second ring were on worlds about 250 light years from Terra. The third ring was established on the borders between the Inner Sphere and the Periphery, 500 light years from Terra. These rings were connected by five lines of forts and castles built on borders between member states. Between the rings were smaller bases. Most of the major bases built on the rings of defenses were also the headquarters of divisions or the home ports of major fleets.
In the Periphery, bases were larger and had stronger defenses. They were also evenly distributed throughout the four realms, each within a short journey of the next.
So there should be a lot of bases out there, even in the Inner Sphere, especially along the 2750-era borders between the Inner Sphere states, as well as on the Periphery border worlds of that time.
Canon bases like Star's End, Niops, New Samarkand, Galtor, Helm and Epsilon Eridani do appear to follow these patterns; the first three are on or near the periphery border, the next two on borders between IS states, and the last only a single jump from Terra. And these were merely the known facilities I could recall off-hand.
